View
220
Download
0
Category
Preview:
Citation preview
7/28/2019 PDF 4.2 Radiation Damage in Biological Systems
1/20
A Look at NuclearScience and Technology
Larry Foulke
Radiation and Realism
4.2 Radiation Damage in Biological Systems
7/28/2019 PDF 4.2 Radiation Damage in Biological Systems
2/20
Nuclear Engineering Program
All three radiation types are capable of ionizingtarget atoms in materials.
What were the three types of radiation?
Lets Review Ionization
Charged particles (protons, electrons, fissionproducts, alpha particles)
Electromagnetic radiation (gamma rays, X-rays)
Neutrons
7/28/2019 PDF 4.2 Radiation Damage in Biological Systems
3/20
Nuclear Engineering Program
All three radiation types are capable of ionizing targetatoms in materials.
Ionization events are the root cause behindALL
observable effects of radiation. Ionization reactions damage materials by breaking chemical
bonds and disrupting normal chemical processes (materialembrittlement, biological damage, etc.).
The rate of ionization (damage) depends on the typeand energy of the radiation, as well as the constituentatoms in the target material.
Lets Review Ionization
7/28/2019 PDF 4.2 Radiation Damage in Biological Systems
4/20
Nuclear Engineering Program
Ionizing Radiations Is radiation that contains enough energy to
remove one or more electrons from an atom ormolecule.
All charged particles are ionizing. Only photons with an energy greater than the ionization energy
of a given atom or molecule are considered ionizing.
Some molecules are affected by photons in the visible or UVrange, but typically only X-rays and gamma rays are considered
ionizing.photon
neutron
chargedparticle
Image Source: See Note 1
7/28/2019 PDF 4.2 Radiation Damage in Biological Systems
5/20
Nuclear Engineering Program
Ionizing Radiations
Neutrons do not have a charge and do not interact withthe electron cloud so they are not able to directly causeionizations.
However, neutron interactions with atomic nuclei canproduce secondary particles that cause ionizations.
Elastic collisions with light (H, C, O, N) nuclei cause thepositively charged nucleus to recoil.
Inelastic collisions or nuclear absorptions produce ionizing rays.
Fission events produce positively charged fission fragments aswell as ionizing rays.
7/28/2019 PDF 4.2 Radiation Damage in Biological Systems
6/20
Nuclear Engineering Program
The number of ionization events that a single particle ofradiation can produce is determined by the energy ofthe radiation.
The ionization density is determined by the LET.
----------------------------------------------------------Relative Relative
Radiation Range LET
----------------------------------------------------------Alpha 1 10,000Beta 100 100Gamma 10,000 1----------------------------------------------------------
Ionization Density
7/28/2019 PDF 4.2 Radiation Damage in Biological Systems
7/20Nuclear Engineering Program
Ionization DensityAverage Human Cell
neutron
gamma ray
x-ray
alpha particle
Separation of ion clusters relative to size of a human cell (conceptualized)
Image Source: See Note 2
7/28/2019 PDF 4.2 Radiation Damage in Biological Systems
8/20Nuclear Engineering Program
Review of Biology 101
An animal is an organized collection of organs, heldtogether by connective tissue, whose functions arecoordinated by a nervous system.
Cells are the basic building blocks of life
Cells are grouped together by specialization into tissues
Tissues work together to form organs, which perform
specific functions Adult humans have approximately 71013 total cells of
210 different types
7/28/2019 PDF 4.2 Radiation Damage in Biological Systems
9/20Nuclear Engineering Program
Cell Functions
All cells perform certain basic tasks:
Metabolism Cells break down complex nutrient molecules to release energy
that is used to enable biochemical reactions within the cell.
Protein Synthesis Protein molecules take part in all biochemical processes in the
cell. Each cell builds proteins required to perform thespecialized tasks of the cell.
Reproduction Cells reproduce by division, referred to as mitosis in eukaryotic
cells.
Every cell contains specialized organelles, which areresponsible for performing these tasks.
7/28/2019 PDF 4.2 Radiation Damage in Biological Systems
10/20
Nuclear Engineering Program
Cell Biology 101
Every cell is 70-90% water
Image Source: See Note 3
1.Nucleolus
2.Nucleus
3. Ribosome
4. Vesicle
5. Rough endoplasmic
reticulum6. Golgi apparatus
7. Cytoskeleton
8. Smooth endoplasmic reticulum
9. Mitochondrion
10. Vacuole
11. Cytoplasm12. Lysosome
13. Centriole
Organelles
7/28/2019 PDF 4.2 Radiation Damage in Biological Systems
11/20
Nuclear Engineering Program
Cell Damage
Ionization can disrupt any of the threemajor functions of cells: Metabolism
Cell may not produce the energy that it needs and dies.
Protein synthesis
Cell may not create protein needed for cell survival. -or-
Cell may not create protein required for its specialized task.
Cell is alive but useless. Reproduction
Cell may not reproduce, or may reproduce incorrectly. Cellremains alive and functioning, but is sterile.
7/28/2019 PDF 4.2 Radiation Damage in Biological Systems
12/20
Nuclear Engineering Program
Cell Damage
Many ionizations within a single cell typically results inenough damage to disrupt metabolism or proteinsynthesis and immediately kill the cell.
For radiation damage, this requires a lot of energy to be
deposited within a single cell: Direct radiation damage
High LET charged particles ionize biological molecules directly.
Indirect radiation damage
High-energy rays produce strongly oxidizing free-radicals byradiolysis. The free radicals then travel through the cell destroyingmolecules. Because cells are mostly water, indirect damage due toradiolysis of water is the most common mechanism.
7/28/2019 PDF 4.2 Radiation Damage in Biological Systems
13/20
Nuclear Engineering Program
Radiolysis of Water
ray
Oxygen
Hydrogen
Electron
Before ReactionPossible
Recombination Products
Free electron
(Charged particle)
H, H- or H+
(Free radical, andcharged particles)
Hydroxyl
(Free radical)
Hydrogen peroxide
(Free radical)
BAD
Other (neutral) products: H2, O
2, H
2O
Hydroperoxyl
(Free radical)
Image Source: See Note 1
7/28/2019 PDF 4.2 Radiation Damage in Biological Systems
14/20
Nuclear Engineering Program
Traumatic Cell Death Cells have redundant features and many types of repairmechanisms to handle biochemical disruptions(otherwise we would never survive!).
Cell death typically requires hundreds of ionizations oroxidations within a single cell.
However, cell reproduction is much more sensitive toionization / oxidation events. One or two events can
disrupt the normal cell cycle.
7/28/2019 PDF 4.2 Radiation Damage in Biological Systems
15/20
Nuclear Engineering Program
What about radiation and DNA? Cells have redundant features and many types of repair
mechanisms to handle biochemical disruptions (otherwise wewould never survive!).
Cell death typically requires hundreds of ionizations or oxidations
within a single cell.
In the human body, approximately 500,000 radioactivedisintegrations occur every minute. (Luckey,Radiation Hormesis,1991)
Every hour on the average, every cell in the human body undergoesapproximately 8000 DNA-modifying events, independentofradiation. (Abelson, P.H.;Science, Vol. 265, 9 September 1994, p.1507)
7/28/2019 PDF 4.2 Radiation Damage in Biological Systems
16/20
Nuclear Engineering Program
DNA DNA is organized into a double-helix shape,
with nucleotide base-pairs between 2phosphate backbones.
The DNA sequence is arranged into bands
called genes. Each gene carries the recipe forone protein.
Humans have 23 pairs of chromosomes (oneset from mom, one from dad).
Pollycove: The body has about 100 trillioncells.
Pollycove: Each cell undergoes about 25,000DNA alternations daily.
Image Source: See Note 4
7/28/2019 PDF 4.2 Radiation Damage in Biological Systems
17/20
Nuclear Engineering Program
Radiation Dose Effects
The amount of energy deposited in amaterial is referred to as radiation dose.
Chronic Dose Dose delivered over an extended period of time.
Acute Dose
Dose delivered over a short period of time.
An acute dose is generally more damaging than a chronic doseof the same size, because the bodys repair mechanisms haveless opportunity to act.
7/28/2019 PDF 4.2 Radiation Damage in Biological Systems
18/20
Nuclear Engineering Program
Short-Term Radiation Effects
Immediate Effects (hours to days) Skin reddening, inflammation
Immune suppression
Sterility
Blood chemistry changes
Loss of hair
Gastrointestinal syndromes
Central nervous system syndromes
IncreasingDose
7/28/2019 PDF 4.2 Radiation Damage in Biological Systems
19/20
Nuclear Engineering Program
Long-Term Radiation Effects
Long term effects (months to years)
Cancer / leukemia
Cataracts
Genetic defects
Blood disorders
Lifespan shortening
Scientific consensus on high dose effects.
Lack of consensus on low dose effects.
7/28/2019 PDF 4.2 Radiation Damage in Biological Systems
20/20
1. Reprinted with permission from DavidGriesheimer, University of Pittsburgh.
2. Public domain:
http://commons.wikimedia.org/wiki/File:Diagram_human_cell_nucleus_no_text.png
3. Public domain:http://en.wikipedia.org/wiki/File:Animal_Ce
ll.svg4. Public domain:http://en.wikipedia.org/wiki/Dna
Image Source Notes
http://commons.wikimedia.org/wiki/File:Diagram_human_cell_nucleus_no_text.pnghttp://commons.wikimedia.org/wiki/File:Diagram_human_cell_nucleus_no_text.pnghttp://en.wikipedia.org/wiki/File:Animal_Cell.svghttp://en.wikipedia.org/wiki/File:Animal_Cell.svghttp://en.wikipedia.org/wiki/Dnahttp://en.wikipedia.org/wiki/Dnahttp://en.wikipedia.org/wiki/File:Animal_Cell.svghttp://en.wikipedia.org/wiki/File:Animal_Cell.svghttp://commons.wikimedia.org/wiki/File:Diagram_human_cell_nucleus_no_text.pnghttp://commons.wikimedia.org/wiki/File:Diagram_human_cell_nucleus_no_text.pngRecommended